1. Field of the Invention
The present invention relates to a circuit and a measuring system.
2. Description of the Background Art
EP 2 354 769 A1, which corresponds to US 20110187351, which is incorporated herein by reference, discloses an angle sensor and a method for determining an angle between a sensor system and a magnetic field. The angle sensor has a magnetic field-generating magnet, which is adjustable with regard to a rotation axis in different rotational positions relative to the sensor system. The sensor system has a first magnetic field sensor for detecting a first magnetic field component, oriented transversely to the rotation axis, and a second magnetic field sensor for detecting a second magnetic field component, situated transversely to plane extending from the rotation axis and the first magnetic field component. The sensor system has a third magnetic field sensor for detecting a third magnetic field component oriented in the direction of the rotation axis.
DE 10 2008 059 401 A1, which corresponds to US 20110291650, discloses a semiconductor chip and a method for generating pulse edges, assigned synchronously to the movement of a mechanical part. A magnetic field is generated and at least two measurement signals for the magnetic field are detected. The magnetic field is changed as a function of the movement of the mechanical part in such a way that the measurement signals are modulated phase-shifted to one another. A first measurement signal is compared with a first reference value. A second measurement signal is compared with a second reference value. The value of the first measurement signal is compared with the value of the second measurement signal. A pulse edge is generated when at least one of these comparisons produces an agreement or the result of the relevant comparison changes its sign.
EP 1 111 392 A1, which corresponds to U.S. Pat. No. 6,965,227, which is incorporated herein by reference, discloses a detection of the rotational speed and angular position of a rotating wheel with an adjustable switching threshold for drift compensation. The detection of the rotational speed and angular position of a wheel occurs by means of a non-contact sensor which scans the wheel and generates a pulse train. The amplitude of the pulse is compared in a comparator with a variable switching threshold. The switching threshold is adjusted so that the value of the difference between the pulse amplitude and the switching threshold does not exceed a predefinable maximum value.
An optical nonius system is known from ELEKTRONIK PRAXIS, No. 18, 17 Sep. 2008, page 22, by J. Quasdorf. The interpolation of analog sine signals is an evaluation function in the case of position sensors. It is possible with a special method to evaluate a number of measurement scales and to combine them to form a position value. Measuring systems are possible thereby that offer a high integral accuracy or very high resolutions with good differential precision. A small optical sensor is sufficient for the scanning.
A rotation angle sensor is known from EP 1 503 182 B1, which corresponds to U.S. Pat. No. 6,894,487, as is illustrated in FIG. 1. The rotation angle sensor has a rotary shaft, a magnet coupled to the rotary shaft, and a magnet-sensitive sensor element. The sensor element generates a sinusoidal and a cosinusoidal output signal as a function of the relative rotation angle between the magnet and the sensor. The rotation angle sensor has an evaluation unit, which generates a signal corresponding to the rotation angle from the output signals. In addition, the shaft is movably guided linearly parallel to its axis along a guide track during its rotation around its axis, so that the distance between the magnet and sensor changes according to a pitch of the guide track. The evaluation unit determines from the output signals of the sensor element a signal from which the distance between the sensor element and the magnet and thereby the number of full rotations of the shaft are determined. A fine signal within a full rotation is determined from the sinusoidal and cosinusoidal output signals and this fine signal is added to the value of the full rotation multiplied by 360°.